1. Field of the Invention
This invention is directed to an air filter, and in particular to an air intake filter for an automobile engine.
2. Description of the Prior Art
In the operation of automobile engines, particularly in the case of high performance engines, a great deal of attention is focussed on the "breathing" of the engine.
In the case of naturally aspirated, "unblown" engines, in which a supercharger is absent, the effective inflow of air into the cylinders significantly influences the performance of the engine. For that reason much effort has focussed on the polishing of valve ports, the degree and timing of valve lift, tuning of the length of intake passages in relation to the location of air flow pressure nodes etc, in order to optimize air flow.
To protect the engine against undue wear it is necessary to filter the incoming air, in order to remove abrasive particles that would polute and damage various portions of the engine.
In many instances, in high performance machines, a filter box of generally rectangular section is provided, having a filter of large cross-sectional area that produces low velocity air flow, with a small presure drop across the filter element. This is thought to improve the breathing performance of the engine.
A major disadvantage of this arrangement is that the filter box is located high up in the engine compartment, and consequently is heated to a significant degree, so as to form an effective heater of the slow moving air within the filter box, thereby effectively reducing the volumetric efficiency of the engine. An existing form of air filter has a conical shaped filter of accordion-pleated, air permeable filter material. The conical filter is aranged with the apex of the cone located upstream, so that air flows from the outside of the cone, inwardly through the divergently inclined filter wall.